Reliable and efficient machine controlled tool positioners or other types of holders for various types of tools are desirable in many different applications and environments. For example, 5-axis numerically controlled machines are used to move tools such as drill bits (and may also move the workpieces themselves) through 3-dimensional space in order to perform the various machining operations desired to shape the workpieces. Given the complicated computer controls and various motors and drives required to move the tools and workpieces, such machines can be relatively expensive. Further, computer programming of the numerical control system can be time consuming and complicated. In some instances, for example, it may be necessary to only approximate the shape of particular curves by extrapolating between specific points on the curves, either requiring the time consuming determination of a large number of points or resulting in a machined curve which may vary slightly from the desired curve.
With particularly large and/or long workpieces, such as structural angle beams or channel beams, free access to move the tool along the length of the workpiece is not always available. In those applications, it has been known to support a suitable tool, such as a torch, for movement in a plane which is substantially normal to the length of the workpiece. For example, Magnuson U.S. Pat. No. 5,256,212 discloses an apparatus which supports a tool (such as a torch) on a ring for movement around the workpiece as the workpiece is moved longitudinally through the ring. The apparatus moves the tool around the workpiece in the two dimensions of the plane of the ring, and the workpiece is moved along its longitudinal length for relative movement between the tool and workpiece in the third dimension. The workpiece may be moved by a gripper connected to a conveyor or by a set of drive rollers which drivably engage the workpiece by squeezing against it.
With such tool supporting apparatuses, cutting by the torch is generally carried out in the center of the ring. A straight longitudinal cut can be provided by positioning the torch in an appropriate position and then moving the workpiece past the torch. A straight lateral cut can be provided by holding the workpiece still and moving the torch over the workpiece in the plane of the supporting ring. Large non-linear contours may be cut by combined movement of the torch around the ring and of the workpiece along its length. Further, for cutting small holes, this may be accomplished by properly positioning the torch and then cutting through the stationary workpiece. In this manner, it is possible to reach the entire surface of the workpiece being processed, whether it is for drilling, punching, burning, cutting or other operations.
However, for some cuts, a more complicated operation can be required. For example, different tools may be secured to the support apparatus depending on the type of operation required. Of course, where different types of operation are required on the same workpiece, the changeover time between tools can significantly reduce the efficient use of the apparatus. Further, the combined cost of different tools can significantly add to the cost of operation.
While a single tool such as a cutting torch may be used for a variety of different operations, thereby obviating the need for multiple tools, the use of a cutting torch for some operations in an apparatus such as noted above can be problematic. For example, when the operation involves cutting larger closed curves (e.g., larger holes), it may be necessary to reverse the direction of longitudinal motion of the workpiece, with such varying workpiece movement requiring relatively high rates of acceleration and deceleration in conjunction with movement of the torch. For example, if a small square hole is to be cut parallel to the longitudinal direction of the workpiece, the workpiece may need to change from a full stop (when the torch is cutting laterally) to full cut speed (when the torch is cutting longitudinally) in a fraction of an inch. At the end of that longitudinal cut, a similarly high deceleration to a stop would be required to change to lateral cutting again. It can be appreciated that a single hole can require a large number of high accelerations and decelerations of the workpiece. Moreover, the smaller the diameter of the corner of the hole, the greater the accelerations and decelerations required.
When such cuts are to be made in heavy materials, such as may be commonly found in structural steel members used in construction, or even in lighter weight materials moving at high speeds, the gear boxes and motors required to provide the necessary accelerations and decelerations can be large and expensive, sometimes impractically so. When the necessary equipment for moving the workpiece is inadequate, however, the holes and corners which are cut can be distorted due to the machine's inability to accelerate the workpiece quickly enough to full cut speed (or stop it quickly enough) during directional changes.
The present invention is directed toward overcoming one or more of the problems set forth above.